simply read history, read philosophy, read ancient comedy..... read anthropology..... look at the commonalities between cultural extremes and sex is often non-discriminatory and opportunistic.
Plato described the Greek custom of having sex with young boys. chimpanzees present the most honest depiction of free/unlimited sex in the animal world but you can see the same desire for sexual gratification in watching female birds in the absence of males of the species, eg ducks.
from the anthropology it can be suggested (trying for a relaxed assertion here) that the more patriarchal a society (that is the more superior the males are in the hierarchy of authority) the more homosexuality is suppressed and this is coupled with male aggression against women and each other. The more equal a society the more "liberated" and natural is sexuality.
Achilles had a loving relationship with his batman, Patroclus.
